Evaporative cooling material

ABSTRACT

Three-layer quilted textile material is suitable for evaporative cooling garments and articles. Superabsorbent layer is a non-woven felt; a blend of cellulose and polyacrylate fibers bonded together to form a non-linting fibrous core. Absorbent layer has inner and outer facings of nylon fabrics for controlled transpiration of water vapor without surface dampness. Cooling material requires immersion in water for one to two minutes and useful cooling time is five to ten hours.

FIELD OF THE INVENTION

This invention relates generally to a sheet material for absorbing,holding, and releasing water and more specifically to sheet materialoptimized for the manufacture of evaporative cooling garments.

BACKGROUND OF THE INVENTION

The discovery that wearing water-soaked clothing cooled the wearerprobably occurred shortly after clothing became standard for humans.While this can be a pleasing effect, for example when backpacking in hotdry weather, it has many drawbacks for every day use.

When outdoors in the sun or a dry breeze; even fully saturated clothingdries quickly. Pouring water over oneself every few minutes is notpractical, except perhaps when walking along a clean brook. Saturated,clinging clothing may look all right during leisure activity, but is notappropriate for a nursery salesperson or policeman.

Much of the water in saturated clothing drips off, both wasting itscooling potential and inconveniencing the wearer by making it risky tohandle papers or go indoors onto a nice floor. Soaking one's clothesrepeatedly can also lead to skin irritation or infection, or footblisters due to shoes made wet by dripping.

Thus, pouring a hatful of water over one's head remained an occasionalchildlike treat until the 1980s or 1990s, when certain classes ofmaterials became available that showed potential for creating morecivilized cooling garments. In the main, these were “superabsorbent”polymer particles (developed for agricultural use); re-useable, encasedsolid/liquid phase-change materials; and advanced synthetic fibers, suchas highly branched polyester filaments and “microfibers”.

All three classes of material have been employed in the construction ofcooling clothing, as well as more complex schemes with self-containedwater supply, pumps, fans, or even Peltier thermoelectric devices.

Polymer particles have been the most popular evaporative coolingmaterial, due to the relative simplicity and cheapness of manufacturingitems that contain them. They are typically used to fill internalpockets or channels provided in garments, especially caps andneckerchiefs. The cap or neckerchief is soaked for up to an hour untilthe particles absorb many times their weight in water, allowed to draina bit, then worn to provide a modest degree of cooling for an hour ortwo opinions differ on the length and quality of cooling these provide.Probably some of the disappointment people sometimes experience withthese products is due to high ambient humidity slowing the evaporationsuch that the cooling is imperceptible, as well as the limited exposureto key thermal zones on the body.

Several attempts were made to fill larger garments such as vests orpants with superabsorbent polymer particles to provide a more effectivecooling. There were several drawbacks with such garments. Mostobviously, the particles swell greatly upon saturation with water. Thepockets or channels into which the particles are inserted must be largeenough to accommodate the swollen “gel” or they may rupture when thegarment is soaked. Thus the garment is heavy and lumpy when moist; baggyand wrinkled when dry.

The dried particles of polymer are free-flowing and settle in the bottomof the generous pockets provided for them. Users are typically warned tomonitor the garment while it is soaking and spread out the particlesperiodically so that they do not just fill and tear the bottom part ofthe pocket and so that the lumps in the garment are no more unsightlythan necessary. While it may be easy enough to soak a bandanna in a bowlof water overnight, spending an hour leaning over the bathtub to help awork jacket puff up properly is not how many people want to start theirday.

Another drawback of polymer particles is that they have littlemechanical strength when hydrated. For this reason, users of clothingcontaining them are told to never wring or squeeze the soaked garment.If the wearer wishes to avoid having his shoes and pants soaked bydripping water, a vest or jacket must be left lying while excess waterdrains away. Once the garment is donned, though, mechanical damage isunavoidable as the wearer fastens a seatbelt and leans back in a vehicleseat, or carries a heavy object against his chest. The ruptured bits ofgel dry to ever-smaller solid particles, which eventually filter throughthe fabric as dust.

A last drawback of using superabsorbent particles to make coolinggarments or blankets is the diffusion rate. The dry particles aretypically one to three millimeters across for ease of handling and toallow for the inevitable breakage. The surface area of particle is smallcompared to its volume, in both its dry and hydrated states. This iswhat makes it necessary to soak even a narrow neckerchief for an hour tofully hydrate the polymer particles. Conversely, the water is evenslower to diffuse back out from the hydrated particle as cooling vapor.This is why some people find that their neck warms the neckerchieffaster than evaporation cools it, especially in humid, still air.

After all, the main motivation for developing superabsorbent polymerswas to retain and immobilize liquids, whether in agricultural soil, in adisposable diaper, or in a wound dressing. Constant, free evaporationfrom the particle surface was not an intended goal, even if it wereachievable. A problem this leads to when polymer particles are includedin a garment or other non-disposable article is that the article oftendoes not dry out fully during one day's use. Not only does thisrepresent lost opportunity for cooling, it leads to mildewing or otherdegradation of the article.

There is great need and demand for cooling garments, for comfort andhealth as well as for improved productivity and performance. One factordriving the search for improved evaporative cooling materials is thecontinuing presence of American and European soldiers in regions withweather that is far hotter than the soldiers are adapted for. Practicaland effective cooling garments, blankets, and other articles could bevitally useful to these soldiers, as well as to others who often mustwork in hot conditions, such as firemen, police, utility linemen, androofers.

Garments that are filled with loose particles of superabsorbent polymerclearly are not a sufficient solution to this need, due to the severaldisadvantages discussed above. Materials have been developed thatattempt to mitigate some of the disadvantages by combiningsuperabsorbent particles with fibrous materials, such as polyesterfiber. The fibrous matrix is intended to hold the particles in place,either by actual attachment or simple entanglement. The absorbentparticles used are typically granules of absorbent polymer as describedabove.

An example of this approach is the published application US2001/0027071A1, now abandoned, of Bumbarger et al. The exemplary insulating andcooling material disclosed is composed of grains of polyacrylamide (oneto two cubic millimeters in volume) embedded in fiberfill (i.e.,non-woven polyester fiber) batting. Bumbarger et al. also suggest thatpolyester fibers may be mixed with “hydrophilic” fibers (composition notdisclosed). The invention appears to have undergone a good deal ofthought and testing to function as a material for high-end evaporativecooling garments intended for “firemen, law enforcement officers,military personnel . . . ” and others working in high heat, butdrawbacks are still evident.

Because the “very tiny” grains of superabsorbent polymer are stabilizedand protected by the fiberfill, the particle size is toward the smallerend of the typical distribution of particles conventionally used forfilling small garments such as neckerchiefs. Bumbarger et al. do notneed to start with large granules to allow for breakage, as discussedabove. Also, because the grains are pre-distributed in the fiber matrix,it is not important to Bumbarger that large granules are easier toinsert in chambers in the garment as it is sewn. Yet even using thissmaller particle size, Bumbarger et al. note that care must be taken toallow sufficient expansion room within the garment to avoid rupture.Thus the garments illustrated in FIGS. 10 and 11 have a markedly bulbousappearance unless covered by a bullet- or fire-resistant shell.

A more serious drawback is that a Bumbarger garment must be soaked 15 to25 minutes to achieve at least 50 per cent of total hydration of thegrains. The Bumbarger reference does not treat this as a great problem;in fact, it is suggested that full hydration is not desirable in mostcases, so as to leave capacity for absorption of perspiration.

Bumbarger et al. suggest that if the cooling garment may be needed in anemergency, it may be stored in pre-hydrated condition or else garmentscould be quick-soaked in heated water inside pressurized vessels. Thisattention to detail is laudable, but it is hard to imagine along-distance cyclist prudently soaking a cooling jacket overnight in aplastic bag on the floor of her tent, or police officers lining up touse the pressure hydrator before going on patrol. Also, if the garmentis worn or even potentially needed every day, it could never be allowedto dry out fully, thus would perhaps have to be stored in a refrigeratoror saturated with antifungal solution instead of pure water so as not tobecome a health hazard due to mold.

It is also desirable that the stock material for evaporative coolinguses such as garments be easy and inexpensive to manufacture and easy tocut and sew. The manner in which Bumbarger et al. introduce the grainsof polymer into the fiberfill batting is not taught, so it is impossibleto evaluate if the manufacturing process is robust or cost-effective. Italso seems likely that grains of polymer would spill out when thematerial is cut and handled, being a nuisance and possibly harmingsewing machines or other delicate equipment.

Additionally, Bumbarger et al. suggest that the inner layer of textilethat is disposed closest to the wearer's body be treated with a moisturebarrier coating, such as BREATHE-TEX®. The importance of this coating tothe invention may be deduced from the fact that claim 1 includes thelimitation of “a coating impervious to liquids while allowing freepassage of gasses therethrough”. Such coatings tend to be expensive andrelatively fragile, subject to mechanical damage and environmentaldegradation. As reported by the International Association of FireFighters on Dec. 15, 1999, several manufacturers of fire fightingapparel with BREATHE-TEX® moisture barrier coating recalled garments dueto degradation of the coating. Their Joint Statement on the issue quotedfrom a letter from the CEO of the company described as “the producer ofthe majority of the moisture barriers being used today” in which the CEOsaid: “investigations suggest that the garments may have been subject toattack resulting from storage conditions, length of service, care and/ormaintenance. [The writer] also indicates there are a number of factorsthat may cause this degradation to occur over time.” One hopes thatmoisture barrier coatings have improved since then, but such a finickycoating, prone to damage from many poorly-understood sources, probablydoes not belong on a garment that is critical to the health of soldiers,police officers, and others unless there is no alternative at all.

Bumbarger et al. have addressed some of the problems associated with useof polymer particles in evaporative cooling material. The fibrous matrixsupporting the particles reduces mechanical damage to the absorbentpolymer, helps maintain the particles in place so that they don't haveto be manually arranged as they swell, and allows use of smallerparticles so that hydration time is possibly as short as 15 minutes (atordinary room temperature and pressure). Using a smaller sizedistribution of particles probably also implies that evaporation ofwater from the particles is correspondingly faster than for conventionalcooling neckerchiefs as have been used since the 1990s. Distributing theparticles evenly throughout the fibrous matrix, instead of loading theminto individual channels, probably makes the cooling effect morepleasant and “convincing” to the body, although the coverage is stillsomewhat spotty.

Cooling garments for extreme conditions have also been made usingpackets of solid/liquid phase change material, thermoelectric cooling,fans and air channels to speed evaporation of sweat, and cooling liquidreplenished periodically or supplied continuously through a hose. Allthese approaches may have applications in which they are practical andmake sense. However, the simplicity and reliability of garments cooledby evaporation of a modest amount of water, potable or not, with norequirement for electricity or other support, is desirable for use inemergencies and in remote or primitive conditions, such as desert camp.

Problems that still remain to be solved to achieve an optimalevaporative cooling material for producing fully practical and desirablecooling garments include: very short hydration time for convenience andresponse to emergencies, thinner and flatter material for better andless intrusive appearance and freedom of movement, and fasterevaporation rate for consistent and effective cooling even in humidatmosphere. With specific regard to the Bumbarger et al. reference, sucha material must be manufactured by a robust process and be reliable anddurable even under hard use or severe conditions.

SUMMARY OF THE INVENTION

The present invention is a three-layer textile material that absorbsliquid water then releases water vapor freely to create evaporativecooling of 15 to 20 degrees F. below ambient. The material is thin,flat, and is easily cut and sewn, so it may be used for the entireconstruction of comfortable garments such as jackets or hats. Thematerial is also useful for cooling blankets for people, food, orequipment; for miscellaneous articles such as beverage containerholders; and for blankets, rest pads, and vests for animals such as dogsand horses.

The sheet material is composed of three layers that are attachedtogether by patterned stitching. The central layer is a non-wovenfibrous felt, or batting, that absorbs water readily and releases it asvapor over a useful period of time. The absorbent felt is typically ablend of three types of fiber: cellulose, a cross-linked polyacrylateco-polymer, and a polyolefin bonding fiber. The fiber blend is largelybiodegradable.

The central fibrous layer is sandwiched between two sheets ofconventional fabric, selected for suitable surface texture, tightness ofweave, and durability. The fabrics are typically two different grades ofwoven nylon.

The cooling sheet material is thin and flat enough to be rolled intobolts for shipping and storage. Garments made from the sheet materialare trim and smooth and are not much different in appearance fromgarments made from conventional fabrics. The sheet material is cut andsewn using industry-standard methods and equipment. No special surfacefinish or coating of the material is needed. Cutting the absorbentmaterial does not release loose fibers, particles, or dust.

The cooling material, or an article made from it, is “activated” byimmersing it in room temperature or cold water for one or two minutes tohydrate the middle absorbent fiber mat. The item can be squeezed toremove excess water and the surfaces can be wiped dry if desired.Evaporative cooling lasts for five to ten hours but varies depending onhumidity, airflow and ambient temperature.

The problems associated with conventional cooling garments oraccessories containing granulated superabsorbent resins, such asdripping, clamminess, powdery deposits on the skin or clothing, lumpsand bulges, spotty cooling, and the long process of immersion andspreading of granules by hand are not experienced when using the novellaminated absorbent material. Except for two minutes of soaking, thecooling garments are nearly as convenient to wear and care for astraditional non-cooling garments.

The absorbent material is especially useful for creating coolinggarments for active sports and work outdoors in hot weather. Garmentsmade from the material are lightweight even when hydrated, soft andnon-chafing, and are re-useable through an indefinite number ofhydration cycles without loss of cooling power.

The invention will now be described in more particular detail withrespect to the accompanying drawings in which like reference numeralsrefer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly cut away, of the evaporativecooling sheet material of the present invention.

FIG. 2 is a cross-sectional view of the material of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view, partly cut away, of the evaporativecooling sheet material 10 of the present invention. FIG. 2 is across-sectional view of material 10 of FIG. 1. Sheet material 10generally comprises three layers of different composition and functionattached together to form a single sheet 10, as will be described fullybelow.

An inner barrier layer 12 is for contact with an item to be cooled, suchas a person. It is typically a sheet of Taslan™ nylon 13, a smooth,shiny fabric that is inherently resistant to wind and water. Inner layer12 protects the skin or clothing from dampness and provides a soft,draping surface for good thermal transfer between sheet material 10 andthe person.

An outer transmission layer 14 is for being exposed to the atmosphereand allowing transmission of water vapor to pass. It is typically madefrom oxford nylon 15, a durable fabric with a coarser weave thanTaslan™, often used for the outer shell of jackets. Oxford nylon 15inherently allows free passage of water vapor and limited passage ofliquid water, due to the size of the openings between threads.

Neither Taslan 13 nor oxford nylon 15 are treated with a surface finish,such as a moisture barrier coating. The ease with which liquid and gaspasses through Taslan 13 and oxford nylon 15 is preferably controlledonly by selection of fabrics of suitable thickness and thread count toprovide the desired properties.

Absorbent middle layer 20 comprises a non-woven fibrous mat 22 that bothwicks liquid water quickly and absorbs and retains water. It has beenfound that a blend of hydrophilic fibers, such as cellulose fibers 24,such as fibers derived from cotton or wood, with superabsorbent fiberssuch as a polyacrylate 25, provides a desirable balance of properties.Cellulose 24 provides rapid uptake of water into fibrous mat 22 thenreleases the water quickly, giving an immediate cooling effect.Cellulose 24 is very effective at transporting water by capillary action(as evidenced by tall trees) and spreads water throughout fibrous mat 22without any need for manipulating sheet material 10 by swishing,squeezing, or massaging.

Polyacrylate 25 is not as efficient at wicking as cellulose 24, but itabsorbs a far greater quantity of water and retains the water well. Byholding water fairly tightly with hydrogen bonds, polyacrylate 25prevents water from being drained out of fibrous mat 22 by gravity andreleases water vapor at a steady rate over a period of hours. Thepolyacrylate 25 composition most preferred is a cross-linked co-polymerof acrylic acid, methylacrylate, and an acrylate/methylacrylate monomerwherein sodium acrylate is substituted for a portion of the acrylicacid. A suitable polyacrylate fiber 25 is produced by TechnicalAbsorbents Limited of the United Kingdom under the name OASIS SAF®.

Water vapor transmission to the atmosphere and hence amount of coolingproduced by sheet material 10 is fairly constant over time until thewater is exhausted, although both amount and duration of cooling areinfluenced by the humidity, air temperature, and movement of air. Theexpected duration of cooling is five to ten hours.

Because absorbent fibers 23 are thin and elongate and have a highsurface to volume ratio, the rate of diffusion into and out of fibers 23is very rapid compared to the rate of diffusion for the one to threemillimeter wide chunks of polyacrylamide or similar granular absorbentused in conventional 20th-century cooling neckerchiefs. Rapid diffusionresults in activation time of two minutes instead of the conventional 30minutes to an hour, as well as a stronger and longer-lasting coolingeffect.

Non-woven mat 22 preferably also includes stabilizing means for holdingthe fibers together, such as a bonding fiber 26, such as a thermoplasticpolyolefin fiber that is softened by heat to create an adhesive forbinding the other fibers 23 into a felt-like mat 22.

The nominal preferred composition of fibers 23,26 to create non-wovenmat 22 is 40% polyacrylate 25, 30% cellulose 24, and 30% bonding fiber.The fibers are bonded together to create a mat 22 that typically has adensity of 120 grams per square meter.

Non-woven mat 22 is sandwiched between inner layer 12 and outer layer 14and attached to them by suitable means as are well known, such as pointbonding or stitching. Alternatively, bonding fiber 26 can be adapted toattach non-woven mat to layers 12, 14 or other adhesive means as knownin the textile field may be used.

Garments made from sheet material 10 are very effective for cooling aperson or animal under most conditions. If additional cooling power isneeded, a garment made from sheet material 10 may also include auxiliarycooling devices, as have been noted above.

Although particular embodiments of the invention have been illustratedand described, various changes may be made in the form, composition,construction, and arrangement of the parts herein without sacrificingany of its advantages. Therefore, it is to be understood that all matterherein is to be interpreted as illustrative and not in any limitingsense, and it is intended to cover in the appended claims suchmodifications as come within the true spirit and scope of the invention.

1. Evaporative cooling material, including: an outer water-vaportransmission layer for providing mechanical protection of said materialwithout substantially hindering the evaporation of water or passage ofwater vapor; an inner moisture barrier layer for providing a smoothinner surface and for blocking transmission of liquid water or vapor;and a middle fibrous absorbent layer disposed between said outer andsaid inner layers, for absorbing applied water and releasing the wateras vapor over a useful time period, thereby causing said inner barrierlayer to be maintained at a temperature substantially cooler thanambient temperature; said fibrous absorbent layer created from a blendof suitable fibers bonded together by suitable bonding means such thatsaid cooling material can be cut without shedding fibers or particles;said outer, inner, and absorbent layers being connected together bysuitable connection means to provide stability of said material.
 2. Theevaporative cooling material of claim 1, said fibrous absorbent layercomprising: a non-woven mat of cellulose and sodium acrylate co-polymerfibers blended in the ratio of approximately three parts cellulose tofour parts acrylate.
 3. The evaporative cooling material of claim 1,said fibrous absorbent layer further including: a suitable bonding fiberfor bonding together all fibers comprising said fibrous layer.
 4. Theevaporative cooling material of claim 1 wherein: said inner barrierlayer blocks water and said outer transmission layer allows passage ofliquid and vapor due to intrinsic properties of the materials selected,including suitable weave density and type, and suitable fibercomposition
 5. The evaporative cooling material of claim 4, said innerbarrier layer being composed of Taslan™ nylon fabric and said outertransmission layer being composed of oxford nylon fabric.
 6. Theevaporative cooling material of claim 1, wherein the component goods areselected such that the evaporative cooling material has propertiessuitable for cutting, shaping, and sewing said material to createevaporative cooling garments